Filter presses, sometimes called “plate-and-frame” filter presses, “membrane” filter presses, or “chamber” filter presses, have been around since the 19th century and are generally used for dewatering processes. They are used to make filter cake products from liquid-solid suspensions or slurries having a large liquid fraction. The solids within the suspensions or slurries typically do not dissolve in the liquid fraction and thus, they are carried in it. Filter presses separate the solids from the liquids, so that the useful part can be processed, packaged or delivered to the next step. One non-limiting example of a prior filter press may be seen in U.S. Pat. No. 5,368,751, which is hereby incorporated by reference.
Filter presses generally work in a “batch” manner. A large number of filter plate assemblies are supported on and are guided along a metal frame. The plurality of filter plate assemblies are forced together using large hydraulic rams, at which point a pump feeds slurry into individual filter chambers which are defined by cavities or recesses between and formed within the faces of each filter plate assembly. The liquid fraction of the slurry (i.e., filtrate) passes through filter cloth provided to each filter plate assembly and into a drainage system, while the solid fraction stays behind in the filter chambers. When the filtration cycle is complete, a batch of solid filtered material, called “filter cake” is produced. The stack of filter plate assemblies is opened, solids are removed from the filter chambers via any one or more of gravity, vibrating, shaking, and/or manual extractors, and then the stack of filter plate assemblies is re-clamped and the filtration cycle is repeated.
In many cases, if a filter cloth gets damaged, for instance by a tear, small hole, wear spot, a fold, or misalignment with the filter plate assembly, the filtrate exiting a particular filter plate assembly will eventually become turbid with solids and the filtering process will be compromised. Higher than allowable turbidity levels can negatively affect downstream processes such as those that use the filtrate in a recycle feed. Higher than allowable turbidity levels can also result in lost profits if the filter cake is the desirable product and a large amount of solids are being discarded with the filtrate. It is, therefore, important to make sure that filter cloths are always functioning properly and not damaged. However, in a conventional filter press having upwards of 150 filter plate assemblies or more, the task of determining which cloth(s) is damaged becomes an incredibly time-consuming task. Each plate typically has two filter cloths thereon, and it can take many hours to visually inspect them all. The small spacing between filter plate assemblies generally requires complete removal of the filter plate assemblies for inspection.
To overcome the above problems, all filter cloths are generally simultaneously replaced at routine predetermined maintenance intervals. While such practices might reduce the chances of filter cloth failure during operation, it is inefficient and costly. More scheduled maintenance time means less production time and reduced operation efficiency. Changing out filter cloths which may still have ample service life cuts into the user's profit margin.